This invention relates to heat dissipation for electronic components.
A DC-to-DC power converter of the kind shown in U.S. Pat. No. 5,987,740, incorporated by reference, for example, includes a heat-generating semiconductor device and a metal base plate that acts as a heat sink to dissipate heat from the device to the outside world.
As shown in FIG. 1, one path 8 for conducting heat from the device 10 to the base plate 12 where it can be dissipated is through silver filled epoxy 14, a lead frame of copper conductors 16, alumina-filled epoxy 18, an alumina piece 20, a copper layer 22 to which the alumina has been directly bonded, and solder 24. The lead frame conductors are soldered to copper runs 23 on the surface of a printed circuit board 25. The assembly is potted in a molding compound 26.
The alumina piece 20 provides a relatively high thermal conductivity for good heat transfer to the base plate and a low capacitance between the copper lead frame and the base plate. A low capacitance is useful in reducing noise in the high-frequency signals that propagate in a DC-to-DC switching power converter.
In another approach, shown in FIG. 2, the heat-generating device 30 has conventional leads 32 that permit surface mounting on copper runs 33 of a printed circuit board 34. Heat is conducted to the base plate 35 along a path 36 that includes the leads, the circuit runs 33 of the board 34, metal columns 42, and a silicone layer 44.
In general, in one aspect, the invention features apparatus that includes (1) a circuit board, (2) a heat dissipator separated from the board by a gap, (3) a heat generating electronic device mounted in the gap, and (4) a heat conducting path between the device and the dissipator. The heat-conducting path includes a path segment that spans the gap at a location adjacent to the device. The path segment includes an electrically insulating material having a thermal conductivity of at least 7 W/m-xc2x0 K.
In general, in another aspect, the heat-conducting path including a path segment that passes along the conductive runs and another path segment that spans the gap at a location adjacent to the device. The other path segment includes by a piece of electrically insulating material that has a thermal conductivity of at least 7 W/m-xc2x0 K.
Implementations of the invention may include one or more of the following features. The device includes a semiconductor power component, e.g., a semiconductor die and a copper base. The electrically insulating material comprises alumina that has a solderable material, such as direct bonded copper, on two opposite faces. The solderable material is soldered to the conductive runs and to the base plate. There are two parallel path segments that span the gap at two different locations adjacent to the device. The device is connected to a lead frame on the board. The device, the board, and the path segment are potted in a molding compound. The heat dissipator comprises a metal base plate.
In general, in another aspect, the invention features a power converter comprising (1) a heat generating power component mounted on a circuit board in a gap between the board and a heat sinking base plate, and (2) two thermally conductive and electrically insulating chimneys mounted adjacent to the device, spanning the gap, and configured to provide parallel paths for conducting heat, which has passed from the device to the board, from the board to the base plate.
Implementations of the invention may include one or more of the following features. Each of the chimneys includes predominantly a non-metallic piece, e.g., alumina that has direct bonded copper on two opposite faces.
In general, in another aspect, the invention features a method that includes conducting heat from a heat generating electronic device that is mounted in a gap between a circuit board and a heat dissipator, the heat being conducted along a path that includes a path segment that passes along conductive runs on the circuit board and another segment that spans the gap at a location adjacent to the device, the other path segment being spanned predominantly by a non-metallic piece that has a thermal conductivity of at least 7 W/m-xc2x0 K.
Among the advantages of the invention are one or more of the following. Heat is removed effectively from the heat-generating device. The alumina thermal chimney provides good thermal conductivity, high dielectric strength and a high dielectric constant. Effective electrical isolation and low capacitance is provided between the heat sink and the circuit. The structure is mechanically rugged and inexpensive to make and is based on well-known manufacturing processes. The structure is shorter than other approaches (e.g., 0.040xe2x80x3 compared to 0.080xe2x80x3) which yields a higher power density for a given converter circuit.
Other advantages and features may be apparent from the following description and from the claims.